Purpose of Equipotential Bonding

Electrical connection of all exposed conductive parts and extraneous conductive parts to maintain the substantially equal potential is called equipotential bonding. The potential equalization between all surfaces which are thus bonded.

Exposed conductive part – A non current carrying conductor in equipment which can be touched and not a live conductor and it may become live conductor during fault condition.

Extraneous conductive part - a conductive part which carry potential include earth potential but not forming in electrical installation.

In a building installation, equipotential bonding conductors shall be interconnected with the following conductive parts:

  •  Protective conductor;
  • Earth continuity conductor; and
  • Risers of air-conditioning systems and heating systems (if any).

The zone is created by connecting all extraneous conductive part by means of equipotential bonding conductor to the main earthing terminal or earth electrode and it is completed by connecting all exposed conductive part to the main earthing terminal by using protective conductor. Such zone is called equipotential zone

1 = Equipotential bonding conductor
2 = Protective conductor
3 = Earthing conductor.
M = exposed conductive parts
P = incoming metallic service
C = extraneous conductive parts
EE= Earthing Electrode

This zone does not mean that voltage cannot exist between conductive parts during faulty condition. The voltage still exists between exposed and extraneous conductive part but voltage will minimize due to the application of bonding.

The extraneous conductive parts that are required to be bonded to the main earthing terminal of the installation (or to the earth electrode of the installation ) include:

a) Gas pipes;
b) Other service pipes and ducting;
c) Risers and pipes of fire protection equipment;
d) Exposed metallic parts of the building structure; and
e) Lightning conductors.

There are two aspects of equipotential bonding

  • Main equipotential bonding – service enters the building
  • Supplementary bonding – bonding within rooms particularly kitchen and bathrooms.

Main equipotential bonding

A main equipotential bonding with a main earthing bar shall be provided near the main service entrance. Connections shall be made to the following parts by bonding conductors:

  •  Lightning conductor;
  • Earthing systems of the electric power distribution system;
  • The central heating system;
  • The conductive water supply line;
  • The conductive parts of the waste water line;
  • The conductive parts of the gas supply; and
  • The structural metal frame-work of the building, (if applicable).

All the bonded pipelines should be metal, if the pipelines are in insulator like plastics, no need to do the bonding.

Supplementary bonding

The supplementary boning or additional are necessary in the location where the increase of electric shock. In domestic premises, the room having bath or shower, kitchens and in the area surrounding of swimming pool is consider as high risk for electric shock.

The following requirements shall be fulfilled:

o The impedance between extraneous conductive parts and the equipotential bonding bar shall not exceed 0 1 Ω.

o All equipotential bonding conductors shall be insulated, the insulation being coloured green-yellow.

o Equipotential conductors between permanently installed extraneous conductive parts and the equipotential bonding bar shall have a cross-sectional area of not less than 4 mm2 copper or copper equivalents.

o The equipotential bonding bar, if any, should have adequate mechanical and electrical properties, and resistance against corrosion.


It should be clearly understood that, there are number of supply other than electrical supply which employ metallic connection near by the conductive parts. During faulty condition, the potential difference between these parts will cause severe electric shock to personnel and also chances to occur arcing between this.

So Equipotential bonding is necessary to eliminate the voltage gradient or difference in voltage potential in exposed conductive parts and extraneous conductive parts.


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